Re: mtdblock mount issue

[Max Stirling <vicky.irobot@gmail.com>]

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Sergei Sharonov wrote:
>> I am trying to mount a cramfs partition from flash. 
>>     
>
> A word of warning. CRAMFS is broken in kernels < 2.6.18. As far as I can tell,
> under heavy load (e.g. reading multiple files in parallel that are not cached)
> it may fail with decompression errors. I think the issue is not exactly with
> cramfs but with some interaction with page cache. Backporting just cramfs files
> to 2.6.15 did not help. If you have drop_caches interface (kernel > 2.6.16 or
> just backport it) it is easy to reproduce. Otherwise it happens _very_
> infrequently because most of the time files are already cached. However the
> consequences are severe - corrupted executables, etc.
> Here is a script to reproduce the problem:
>
> ===============================================
> # Copy large file from cramfs to tmpfs
> cp /bin/smbd /tmp/
>
> # First concurrent access to files/directories 
> while [ 1 ]; do cat /bin/* > /dev/null; done &
>
> # Second concurrent access to test file and cache flush
> for((i=0;i<99999;i++)) do echo -n "cycle=$i "; 
>   cmp /bin/smbd /tmp/smbd ; 
>   echo 3 > /proc/sys/vm/drop_caches ; 
> done
> ===============================================
>
> Note that /bin is in cramfs. smbd can be any large file.
> I've also seen statements that drop_caches interface is not 100% reliable.
> Nevertheless I have experienced decompression errors even without forcing 
> cache purge.
> Above script has caused failures on PowerPC/2.6.16 and ARM9/2.6.15.
> 2.6.18 and 2.6.23 seem ok.
>
> Regards,
>
> Sergei 
>
> P.S. Yes, cramfs has little to do with MTD but since ppl here use it with flash
> I felt it was a good idea to post this warning.
>
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
>   
thanks for the info. I think I will check out squashfs then.

But before that I wanted to fix the issue that I am seeing. There might 
be something wrong in my implementation?

BTW I thought this was the right mailing list, since I am trying to 
mount cramfs image using MTD. Can you point me to the right mailing list?


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